The present invention has been conceived in the course of development of an apparatus for applying hot mix, examples of which are described in the applicant's Australian patent application no. 2006297059 (hereinafter referred to as “the earlier application”). For the most part, the background to the present invention is set out in the specification of the earlier application and need not be repeated here.
In conventional practice, the surfaces of tar-sealed roads are covered by a layer of material comprising a mix of what is known as “aggregate” and bitumen. (When used in this specification, the term “mix” will refer to a mixture of these materials that is suitable for building and repairing roads, unless it is clear from the context that another meaning is intended). The aggregate comprises stone particles of various graded sizes. If the mixing has been properly carried out, the stones are randomly dispersed in a matrix of the bitumen and the bitumen should be bonded to each stone and should cover as much of the surface of the stone as possible. It is of course nearly impossible to achieve such an ideal mix in practice but it is at least a goal that is aimed at.
The apparatus disclosed in the earlier application comprises, inter alfa, an uprightly disposed, cylindrical vessel incorporating a mixing chamber arranged to receive aggregate and bitumen, heating means arranged to heat the aggregate and bitumen, and mixing means for mixing the aggregate and bitumen to form a hot mix. The heating means disclosed comprises a gas ring mounted in what is effectively a combustion chamber located below the mixing chamber. The vessel comprises a separating element which separates the combustion chamber from the mixing chamber, serving as both the floor of the mixing chamber and what will be called herein the “roof” of the combustion chamber. For reasons that are discussed in the earlier application, the separating element is advantageously dome shaped. The heating means comprises a gas ring positioned adjacent the periphery of the separating element so that the heat from the burning gas is spread evenly over the separating element.
In some jurisdictions, it has emerged that oil, particularly but not exclusively diesel oil, is preferred to gas as a fuel and it is an object of the present invention to provide an apparatus in which oil can be used for heating the hot mix. To achieve this object, the operational parameters of oil burners must be taken into account. In this regard, it is considered impossible, or at least economically and/or technically impractical, to provide oil burners arranged in a ring as a simple substitute for a gas ring for apparatus such as disclosed in the earlier application.